* The reference bandwidth used in the OSPF cost calculation is 40 Gbps

* The reference bandwidth used in the OSPF cost calculation is 40 Gbps

* Networks and interfaces are added to an OSPF instance under the interface configuration mode.

* Networks and interfaces are added to an OSPF instance under the interface configuration mode.

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* An OSPF can be configured as a decimal or in decimal dotted notation, but it is always displayed in decimal dotted notation in the configuration and in '''show''' commands.

* Passive interfaces are applied to the interface as opposed to under the OSPF instance.

* Passive interfaces are applied to the interface as opposed to under the OSPF instance.

* If a router ID is not manually configured, the loopback 0 IP address is always preferred. If loopback 0 does not exist, Cisco NX-OS selects the IP address for the first loopback interface in the configuration. If no loopback interfaces exist, Cisco NX-OS selects the IP address for the first physical interface in the configuration.

* If a router ID is not manually configured, the loopback 0 IP address is always preferred. If loopback 0 does not exist, Cisco NX-OS selects the IP address for the first loopback interface in the configuration. If no loopback interfaces exist, Cisco NX-OS selects the IP address for the first physical interface in the configuration.

Revision as of 21:13, 8 March 2010

Objective

This tech note outlines the main differences in Open Shortest Path First Version 2 (OSPFv2) support between Cisco® NX-OS Software and Cisco IOS® Software. Sample configurations are included for Cisco NX-OS and Cisco IOS Software for some common features to demonstrate the similarities and differences. Please refer to the NX-OS documentation on Cisco.com for a complete list of supported features.

OSPF Overview

OSPFv2 is an IETF (RFC 2328) standards-based dynamic link-state routing protocol used to exchange network reachability within an autonomous system.

Important Cisco NX-OS and Cisco IOS Software Differences

In Cisco NX-OS:

OSPF command-line interface (CLI) configuration and verification commands are not available until you enable the OSPF feature with the featureospf command.

Eight equal-cost paths are supported by default. You can configure up to sixteen.

The reference bandwidth used in the OSPF cost calculation is 40 Gbps

Networks and interfaces are added to an OSPF instance under the interface configuration mode.

An OSPF can be configured as a decimal or in decimal dotted notation, but it is always displayed in decimal dotted notation in the configuration and in show commands.

Passive interfaces are applied to the interface as opposed to under the OSPF instance.

If a router ID is not manually configured, the loopback 0 IP address is always preferred. If loopback 0 does not exist, Cisco NX-OS selects the IP address for the first loopback interface in the configuration. If no loopback interfaces exist, Cisco NX-OS selects the IP address for the first physical interface in the configuration.

Neighbor adjacency changes are not logged by default. The log-adjacency-changes CLI command is required under the OSPF instance.

When interface authentication is configured, the OSPF key is encrypted with Data Encryption Standard 3 (3DES) in the configuration. Cisco IOS Software requires the service password command.

When you rollover an OSPF authentication key in a combined Cisco NX-OS/Cisco IOS network, you should configure both keys on the Cisco NX-OS router to ensure that there is sufficient overlap between the old key and the new key for a smooth transition to the new key. You should configure the new key as a valid accept key on all the NX-OS and IOS routers before the new key becomes a valid generation key in the keychain. During the overlap period, Cisco NX-OS transmits the new OSPF key and accepts OSPF authenticated packets from both the old key and the new key.

Things You Should Know

The following list provides some additional facts about Cisco NX-OS that should be helpful when designing, configuring, and maintaining an OSPF network.

Four OSPF instances can be configured per virtual device context (VDC).

Numerous Virtual Route Forwarding (VRF) instances can be associated with an OSPF instance.

If you remove the featureospf command, all relevant OSPF configuration information is also removed.

The shutdown command under the OSPF process can be used to disable OSPF while retaining the configuration. Similar functionality can also be applied per interface with the ip ospf shutdowncommand.

The show running-config ospf command displays the current OSPF configuration.

An OSPF instance can be restarted with the restart ospf <instance #> command.

OSPF is the only layer 3 routing protocol that supports stateful process restart.

You cannot configure multiple OSPF instances on the same interface.

An interface can support multi-area adjacencies using the multi-area option with the router ospf interface command.

Secondary IP addresses are advertised by default, but can be suppressed per interface.

Configuration Comparison

The following sample code shows configuration similarities and differences between the Cisco NX-OS and Cisco IOS Software CLIs. There are two significant differences: Cisco NX-OS allows OSPF to be enabled and disabled globally, and it has a more interface-centric configuration that makes it easier to read.

Cisco IOS CLI

Cisco NX-OS CLI

Enabling the OSPF Feature

Cisco IOS Software does not have the ability to enable or disable OSPF.